Data communication system and method

ABSTRACT

A data communication system includes one or more data processing units and includes a central control unit. The decentralized data processing units are connected to the central control unit by data connection. The central control unit includes a synchronisation unit for outputting via the data connection an synchronisation signal to the data processing unit. The data processing unit includes a data generator for generating data and transmitting, after the synchronisation signal, data to the central control unit.

FIELD OF THE INVENTION

This invention relates to a data communication system. The inventionfurther relates to a central control unit. The invention also relates toa data processing unit, and to a vehicle. The invention further relatesto a method for communicating data. The invention further relates to acomputer program product.

BACKGROUND OF THE INVENTION

From United States Patent Application Publication US 2006/0080495, adata communication system is known. The data communication system has acentral control unit, decentralized data processing units and a dataconnection between the central control unit and the decentralized dataprocessing units. During the transmission, in order to request datapackets, the central control unit periodically outputs synchronizationpulses over the data connection to the data processing unit interface,whereupon the decentralized data processing unit transmits data packetsto the central control unit. The decentralized data processing unitgenerates an electrical discharge pulse after the synchronization pulsebut before the transmission of a first data packet, therebycounteracting an electrical charging of the data processing unitinterface by the synchronization pulse.

However, a disadvantage of the data communication system described inthis Patent Application Publication, is that it consumes a significantamount of power. In particular the synchronisation pulse as well as thedischarge pulse consume a significant amount of power. Furthermore, aseparate power supply is required to generate the synchronisation pulse.

SUMMARY OF THE INVENTION

In accordance with the present invention a data communication system, acentral control unit, a data processing unit, an occupant protectionsystem is provided, a vehicle, a method for communicating data and acomputer program product as described in the accompanying claims areprovided.

Specific embodiments of the invention are set forth in the dependentclaims.

These and other aspects of the invention will be apparent from andelucidated with reference to the examples of embodiments describedhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects and embodiments of the invention will bedescribed, by way of example only, with reference to the attacheddrawings.

FIG. 1 schematically shows a block diagram of an example of anembodiment of a data communication system.

FIG. 2 schematically shows examples of graphs of signals that may betransmitted by the example of FIG. 1.

FIG. 3 schematically shows a circuit diagram of an example of anembodiment of a central control unit.

FIG. 4 schematically shows a circuit diagram of an example of asynchronisation unit.

FIG. 5 schematically shows a circuit diagram of an example of anembodiment of a data processing unit.

FIG. 6 schematically shows a block diagram of an example of anembodiment of a restraint system.

FIG. 7 schematically shows a top view of an example of a vehicle with arestraint system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, an example of a data communication system 1 is shown. Thedata communication system 1 includes a central control unit 10 and oneor more, in this example two, data processing units 20. The datacommunication system 1 further includes one or more data connections30,31. The data connections 30,31 connect the data processing units 20to the central control unit 10. As shown in FIGS. 4 and 5 in moredetail, the data connection 30,31 may be connected to a power source Vsto provide power to the data processing units 20.

As shown in FIG. 3 in more detail, the central control unit 10 mayinclude one or more synchronisation units 11. The synchronisation unit11 may output via the data connection 30,31 a synchronisation signal toone or more of the data processing units 20. By means of thesynchronisation signal, the time-base of the data processing units 20can be synchronised. As shown in FIG. 5 in more detail, the dataprocessing unit 20 may include a data generator 22. The data generator22 can generate data and transmit the data to the central control unit10, for example in order to transmit information obtained by a sensor orother suitable information to the central control unit 10.

The synchronisation unit 11 may output the synchronisation signal bychanging an energy state of the data connection from a current energylevel to a lower energy level and changing an energy state from thelower energy level back to current energy level. Thus, the energy levelof the data connection is reduced when outputting the synchronisationsignal. Hence, the consumption of energy by the data connection, andaccordingly the power consumption of the system may be reduced.Furthermore, charging of capacitive elements, e.g. in the dataconnection 30,31 or in the data processing units 20, by thesynchronisation signal may be prevented. Accordingly, the need toprovide a discharge signal after outputting the synchronisation signalmay be obviated. For example, as explained below in more detail withreference to FIG. 2, the voltage level V_(L) of the data connection 30may be changed from a steady state voltage V_(DC) to a, lower,synchronisation signal voltage V_(sync).

FIG. 2 schematically illustrates an example of the development (as afunction of time) of the voltage V_(L) of the data connection 30, thecurrent I_(s) originating from the data processing unit 20, the currentI_(c) originating from the central control unit 10 and the total currentI_(T) flowing through the data connection 30. As shown in FIG. 2, thesynchronisation unit 11 may output a synchronisation signal SYNC to thedata processing units 20 connected to the data connection 30,31. Thesynchronisation signal SYNC may, for example, be outputted periodically,such as after a period of time above 0.1 milliseconds and below 1millisecond, such as 0.5 milliseconds or less, for instance every 0.25milliseconds. It should be noted that, for illustrative purposes, theduration of the synchronisation signal SYNC is exaggerated in FIG. 2. Asshown in the example of FIG. 2, the synchronisation signal SYNC may forexample be a negative voltage pulse. In the example of FIG. 2, thenegative voltage pulse is superimposed on a DC voltage level. (It shouldbe noted, that since the voltage pulse is negative, the superpositionresults in a lowering of the voltage level V_(L) of the data connection30). The DC voltage level may for example be a DC offset voltagesuitable to supply power to the data processing units 20. The voltage ofthe DC offset voltage may for example be in the range from 5 to 7 volts,such as 6 volts for instance. The voltage of the synchronisation signalSYNC may for example be a voltage less than the DC offset voltage forexample between 5 to 7 volts less, such as 6 volts lower than the DCoffset voltage. However, other voltages may also be used.

As shown in FIG. 2 with the dashed line II, when a positivesynchronisation pulse would be used, and without discharging signal, thereturn of the voltage of the data connection 30 to the DC offset levelwould be delayed. The delay is caused by the charge on the dataconnection 30 and the time required to discharge the data connection 30after the synchronisation signal SYNC has been sent. However, in casethe energy level of the data connection is lower during outputting ofthe synchronisation signal SYNC than the energy level before theoutputting of the synchronisation signal SYNC, e.g. in the steady state,charging of the data connection by the synchronisation signal may beprevented. Hence the need to provide a discharge signal at the end ofthe synchronisation can be obviated.

As shown in FIG. 2, to output the synchronisation signal SYNC, forexample the energy level, e.g. the voltage V_(L), of the data connection30 may be lowered. To accelerate the lowering of the energy level of thedata connection 30, the synchronisation unit 11 in the central controlunit 10 may enable a current Ic to flow, during a period of time denotedwith I in FIG. 2, through the data connection 30 at the start of thesynchronisation signal. Thereby, the data connection 31 can bedischarged and the lowering of the voltage level of the data connection31 to the lower, synchronisation signal voltage level V_(SYNC) can befacilitated. After the voltage of the data connection 31 has returned tothe steady state voltage level V_(DC), the respective data processingunit(s) 20 may transmit data, during a period of time denoted with IIIin FIG. 2, to the central control unit 10. As shown in the example ofFIG. 2, the data processing unit 20 may transmit one or more binarysignals over the data connection 30. In this example, the dataprocessing unit 20 transmits a pulsed current I_(s) and the binarysignal is formed by the current pulse. The current pulse and/or thedischarging current may for example be currents flowing from the dataprocessing unit 20 towards the central control unit 10 or vice versa.

The central control unit 10 may be implemented in any manner suitablefor the specific implementation. An example of an embodiment of acentral control unit 10 is shown in FIG. 3. The central control unit 10may, as shown in FIG. 3, include a synchronisation control unit 11.

The synchronisation unit 11 may implemented in any manner suitable forthe specific implementation. The synchronisation unit 11 may for examplebe arranged to output the synchronisation signal by changing a voltageof the data connection from a first level, for example a DC offsetvoltage to a second, lower, level and back, from the second level to athird level higher than the second level. The third level may forexample be the same as the first level, or be higher than the firstlevel or be lower than the first level. As shown in FIG. 3, thesynchronisation control unit 11 may for example include a timer 12, anda synchronisation signal generator 13. In the example of FIG. 3 thesynchronisation signal generator 13 is connected with a signal generatorinput 130 to a clock signal output 120 of the timer 12. Thesynchronisation signal generator 13 is further connected with agenerator output 131 to the data connection 30. In this example, thetimer 12 periodically outputs a clock signal. Based on the clock signalreceived from the timer 12, the synchronisation signal generator 13outputs a synchronisation signal at the generator output 131.

The synchronisation signal generator 13 may be implemented in any mannersuitable for the specific implementation. The synchronisation signalgenerator 13 may, as for example shown in FIG. 3, include two or moredifferent voltage supplies Vs1,Vs2 which are at different voltages, anda switch S13 which can connect a selected voltage supply to thegenerator output 131. In the example of FIG. 3, for instance, the switchS13 is connected with a first contact at a first switch side to the lowvoltage supply Vs1 and with a second contact at the first switch side tothe high voltage supply Vs2. (For illustrative purposes, the voltagesupplies Vs1,Vs2 are shown in FIG. 5 connected to ground GND viarespective capacitors C11,C12.) The high voltage supply Vs2 is at ahigher voltage than the low voltage supply Vs1. A contact at a secondside of the switch S13, opposite to the first switch side, is connectedto the generator output 131, in this example via a resistor R13.Depending on the state of the switch S13, the first contact or thesecond contact is electrically connected to the contact at the oppositeside, and hence either the first voltage supply Vs1 or the secondvoltage supply Vs2 is connected to the contact at the second side of theswitch, and hence to the signal generator output 131. The state of theswitch S13 is controlled by the clock signal inputted at the signalgenerator input 130. In case the clock signal is low, the high voltagesupply Vs2 is connected to the generator output 131. In case the clocksignal is high, the low voltage supply Vs1 is connected to the generatoroutput 131. Hence, the voltage of the signal generator output 131 iscontrolled by the clock signal and the synchronisation signal may begenerated by the synchronisation signal generator 13. As illustrated inFIG. 3, the inputted signal may have a pulsed shape, and accordingly,the voltage of the signal generator output 131 may change in a pulsedmanner.

As shown in the example of FIG. 3, the data communication system 1 mayinclude a discharging unit 14. The discharging unit 14 may output adischarge signal over the data connection 30,31. The discharge signalmay discharge the data connection 30,31 and/or the interface of therespective data processing unit(s) 20 connected to the data connection30,31 over which the discharge signal is sent. Thereby the lowering ofthe energy level of the data connection 30,31 can be accelerated.

For instance, in case the synchronisation signal is a voltage signal,such as a voltage pulse, the voltage of the data connection 30,31 willdeviate from the steady state voltage V_(DC) during transmission of thesynchronisation signal. The steady state voltage V_(DC) may, forexample, charge capacitances in the data connection 30,31 or in the dataprocessing units 20. In the circuit diagram shown in FIG. 5, forinstance, the capacitive elements are represented, for illustrativepurposes, by a separate capacitor C20. However, the capacitance may alsobe an integral part of, for example, the data connection 30 or the dataprocessing unit 20 and not be present as a separate element but forexample caused by inherent, parasitic, capacitances. Due to the steadystate voltage V_(DC), the data connection 30,31 and/or the respectiveinterfaces between the data connection 30,31 and the data processingunits 20 may be charged. Accordingly, the time required to discharge thecharged components delays the lowering of the voltage of the dataconnection to the synchronisation signal voltage V_(SYNC), and hence mayincrease the duration of the synchronisation signal SYNC. Bytransmitting the discharge signal, the discharging can be acceleratedand, for example, the duration of the synchronisation signal SYNC may bereduced.

The discharging unit 14 may be implemented in any manner suitable forthe specific implementation. The discharging unit 14 may for example bepresent in the central control unit 10 or the data processing unit 20.The discharging unit 14 may for instance output a discharge signal fromthe central control unit 10 to the data processing unit 20 via the dataconnection 30,31. For instance, as shown in FIG. 3, the discharging unit14 may be present in the central control unit 10. The discharging unit14 may include a switch S14 which connects the data connection 30 via acurrent source I to a node at a voltage lower than the steady statevoltage V_(DC), for example, to ground GND. The discharging unit 14shown in FIG. 3 further includes a switch control 141. The switchcontrol 141 closes the switch S14 via a switch control input 143. Theclosed switch S14 allows the current source I to draw current from thedata connection 30 and hence discharging the data connection 30.However, the discharging unit 14 may also be implemented in a differentmanner, and for example include a current source which can be switchedon and off and which draws a current from the data connection 30, whenswitched on.

The operation of the discharging unit 14 may be coordinated with respectto the operation of the synchronisation signal generator 13. Thereby,the data connection 30 may be discharged a short period of time afterthe transmission of the synchronisation signal is started and the periodof time available for transmission of the data from the data processingunits to the central control unit may be increased. For instance, thedischarging unit 14 may discharge the data connection in response to theclock signal. In the example of FIG. 3, the switch control 141 isconnected to the clock 12 and can receive the clock signal via thedischarging unit input 140. The switch control 141 closes the switch S14in the discharging unit 14 in response to the clock signal. However, thedischarging may also be coordinated with respect to the synchronisationsignal in another manner. For instance, in the example of FIG. 3, theswitch S14 may be closed in response to switching of the synchronisationsignal generator 13 from the high voltage supply Vs2 to the low voltagesupply Vs1.

The signal generator 11 may, as shown in FIG. 4, include a comparingunit 15. As shown in FIG. 4, a first comparing unit input 150 of thecomparing unit 15 may be connected to a reference source (not shown inFIG. 4) which provides a reference signal representing the desiredoutput voltage of the synchronisation unit 11. At the first comparingunit input 150 a pulsed reference signal may be inputted, for examplewith pulses at regular time intervals.

The comparing unit 15 may for example include a comparator which isconnected with a first input to a signal source which provides areference signal and which is connected with a second input to the dataconnection 30 and outputs a binary signal, e.g. either a positive signalor a negative signal with a constant amplitude. The comparator may forexample output the positive signal in case the voltage at the firstinput is higher than the voltage at the second input and output thenegative signal in case the voltage at the first input is lower than thevoltage at the second input. In such case, in case the voltage of thedata connection 30 exceeds the reference signal, the negative signal isoutputted by the comparator and in case the voltage of the dataconnection 30 is lower than the reference signal, the positive signal isoutputted by the comparator. Accordingly, outputting of thesynchronisation signal and the discharging signal can be controlled.

The synchronisation unit 11 may output the discharge signal based on thesensed parameter. As shown in the example of FIG. 4, the comparing unit15 may for instance control an output stage of the synchronisation unit11 based on the sensed parameter. In the example of FIG. 4, the outputstage includes a push-pull output stage. The control inputs of thepush-pull stage are formed by the control terminals G10 and G20 oftransistors T10,T20. The transistors T10,T20 connect the data connection30 to a power supply Vs and to ground, respectively. The transistorsT10,T20 are connected to each other with respective terminals D10 resp.D20 at a node V11 which is also connected to the data connection 30. Aterminal S10 of a respective transistor T10 is connected to the powersupply Vs and a terminal S20 of a respective transistor T20 is connectedto ground. In the example of FIG. 4, an output 152 of the comparing unit15 is connected to control inputs G10,G20 of the output stage of thesynchronisation unit 11. The output signal of the comparing unit 15controls the output stage, and hence the voltage and/or current of thedata connection 30.

The transistors T10,T20 of the push-pull output stage may for example beoperated in active mode. With the signal presented at the comparing unitoutput 152, the control terminals G10,G20 of the transistors T10,T20 canbe controlled, and accordingly the voltage drop between an inputterminal S10, D20 and an output terminal D10,S20 of a respectivetransistor T10, T20 can be regulated, as well as the current flowingbetween the input terminals and the output terminals. Thereby thevoltage of the data connection 30 can be controlled, as well as thecurrent flowing from the data connection 30 to ground GND via thetransistor T20.

In the example of FIG. 4, the transistors T10,T20 are connected suchthat they form a push-pull regulator. In case the output of thecomparing unit 15 increases, the voltage drop over the first transistorT10 decreases and the voltage drop over the second transistor T20increases, and hence the voltage of the data connection 30 increases. Incase the output of the comparing unit 15 decreases, the voltage dropover the first transistor T10 increases and the voltage drop over thesecond transistor T20 decreases. Hence the voltage of the dataconnection decreases. Furthermore, in case the output of the comparingunit decreases, the current through the second transistor T20 increases,and hence the data connection 30 can be discharged. Hence, the comparingunit output controls the synchronisation signal and the discharge signalsimultaneously.

The synchronisation unit 11 may include a sensor for sensing a parameterof the data connection 30,31 and/or the data processing unit 20. Thesensor may for example include a voltage sensor which can sense thevoltage of the data connection 30 or any other type of sensor suitableto sense the desired type of parameter of the data connection 30. Thesynchronisation unit 11 may for instance include a circuit in which thesensor, and/or the synchronisation signal generator and/or the dischargesignal generator are combined. In the example of FIG. 4, for instance,the circuit includes the comparing unit 15 and the push-pull stage. Inthe example of FIG. 4, a second comparing unit input 151 of thecomparing unit 15 may be connected with a feedback line 153 to the dataconnection 30,. The comparing unit 15 can thus sense a parameter of thedata connection 30 and forms a sensor. Accordingly, the second comparingunit input 151 forms a sensor input 151 and the data connection 30 isconnected to the sensor input 151 to sense a parameter of the dataconnection 30.

The synchronisation unit 11 may for example be arranged to control themagnitude of the discharge signal and/or the synchronisation signalbased on a sensed parameter, e.g. the sensed voltage, of the dataconnection 30. Thereby, a more accurate control of the discharge signalmay be obtained and the duration and or magnitude of the dischargesignal may be reduced. The amplitude of the discharge signal and/or thesynchronisation signal may for example be controlled to be linearly ornon-linearly dependent on the difference. The comparing unit 15 may forexample include a differential amplifier which is connected with apositive input to a signal source. The signal source may provide areference signal and be connected with a negative input to the dataconnection 30. Thereby, the amplitude of the signal outputted by thecomparing unit 15 (which may be used to control the push-pull stage, asshown in the example) may be proportional to the difference between theamplitude of the reference signal and the voltage of the data connection30.

In the example of FIG. 4, by means of the second comparing unit input151, the voltage at the first data connection 30 can be sensed by thecomparing unit 15. In this example, the comparing unit 15 senses thevoltage of the data connection 30, which is fed back to the comparingunit input 151 via a feedback line 153. The comparing unit 15 comparesthe sensed voltage with a reference voltage inputted at the first inputs150 and outputs a signal which is linearly proportional to thedifference between the sensed voltage and the reference voltage. Theoutput signal of the comparing unit 15 is inputted to the controlterminals G10, G20 of the push-pull output stage and thereby the voltageof the synchronisation signal and the current of the discharge signalare controlled together and simultaneously.

In the example of FIG. 4, the voltage of the data connection 30 and thecurrent flowing from the data connection to ground GND are controlled asa function of the voltage on the data connection 30 (and, in thisexample, the reference voltage). Thereby, the data connection may bedischarged in a controlled manner and in short period of time, since theneed to account for possible differences in voltage and/or duration ofthe synchronisation signal is obviated. In case, for example, the sensedvoltage is below the reference voltage, the comparing unit 15 willcontrol the control terminals G10,G20 to increase the voltage dropbetween the node V11 and ground GND and to decrease the voltage dropfrom the power supply Vs to the node V11. (For example by increasing theconductance from one terminal D10 to another terminal S10 and/ordecreasing the conductance between the node V11 and ground GND) In case,for example the sensed voltage is above the reference voltage, thecomparing unit 15 will control the control terminals G10,G20 to decreasethe voltage drop between the node V11 and ground GND (for example byincreasing the conductance from one terminal D20 to another terminal S20and/or decreasing the conductance between the voltage supply Vs and thenode V11 and hence allowing more current to flow from the dataconnection 30 to ground GND). The control will further increase thevoltage drop from the power supply Vs to the node V11.

FIG. 5 schematically shows an example of a data processing unit 20,which may be used in the example of FIG. 1. The data processing unit 20may include one or more other sources of data. The data processing unit20 may, as shown in FIG. 5, include a data generator 22 which generatesdata to be transmitted to the central control unit 10. The datagenerator 22 may for example include one or more sensors. However, thedata processing unit 20 may include other types of data generators, andthe invention is not limited to applications in sensor systems. Thesensor may for instance include an acceleration sensitive sensor, suchas an acceleration or deceleration sensor which may be used in anoccupant protection system in a vehicle, such as a motor vehicle.However, other types of sensor may be used, such as for instance apressure sensor, a temperature sensor which can detect, for instance, atemperature increase in a cavity which is compressed during an accident,such as the space inside the door of a motor vehicle.

The data connections 30,31 may, as explained above, be electricalconnections. For example, a data connection 30 may be set to a highvoltage and the other data connection 31 may be set to a low voltage,that is: a voltage lower than the high voltage. In the example of FIG.1, for instance a data connection 31 acts as ground (e.g. is set to zerovolts) whereas the other data connection is set to a suitable supplyvoltage. Thereby electrical power can be supplied to the data processingunits 20,21 over the same line as used to transmit the data. As shown inFIG. 5, the data connection 30 may for instance be set to a high voltageand connected to a power supply contact 210 of the data generator 22 aswell as to a signal input 211 thereof.

The data processing unit 20 may include a data transmitter 21, which inthe example of FIG. 6 includes a current source 12 and a controllableswitch S20. The switch S20 can alternately enable and inhibit the flowof current from data connection 30, via source 12, in this example toground. The state of the switch is controlled via a switch control input212 which is connected to the sensor 22. By alternately opening andclosing the switch, the current through the data connection 30 can becontrolled, and hence a current signal be transmitted to the centralcontrol unit 10.

The data processing unit 20 may include a signal inverter 222. The datagenerator 22 may be connected to the data connection 30 via the signalinverter 222. For instance, as shown in FIG. 5, the signal input 211 ofthe data generator may be connected to the signal inverter output 2222,and hence be indirectly connected to the data connection 30.

The signal inverter 222 may output a signal of a first level when thesynchronisation signal is inputted to the signal inverter and outputtinga signal of a, higher, second level when the synchronisation signal isnot inputted to said inverter. The signal inverter 222 may, as forinstance in the example of FIG. 5, include an inverting amplifier. Theinverting amplifier IA222, may for example be connected with a negativeamplifier input IA− to the data connection 30, via an inverter input2220. A positive input IA+ of the amplifier IA222 may be connected to anamplifier output 222. In the example of FIG. 5, the positive input IA+is indirectly connected to the amplifier output 222. The amplifieroutput is connected to a control input of a controllable current source,in this example a transistor T22. As shown in FIG. 5 with the dashedline, the transistor T22 may be connected with a terminal to a voltagesupply, formed in FIG. 5 by the data connection 30 and with an oppositeterminal to an output 2222 of the signal inverter 222. The oppositeterminal is connected to the positive amplifier input IA+, via a voltagedivider, which in this example includes two resistors R220, R221 inseries which connect the opposite terminal to ground. A node between theresistors R220, R221 is connected to the positive amplifier input IA+.

The data processing unit 20 may include an energy storage 23 connectedto the data connection 30 for storing energy. The energy storage 23 maybe connected to the data generator 22. For example, in FIG. 5 the energystorage 23 is connected with a power input/output to the data connection30 and to the power supply contact 210. The energy storage may releasethe stored energy to the data generator when the synchronisation signalis received by the data processing unit. For example, as shown in FIG.5, the energy storage may include a (or more than one) capacitiveelement C23 which stores energy during the steady state, e.g. by beingcharged, and releases energy, e.g. discharges, and hence provide acurrent, when the supply voltage, that is the voltage over the dataconnection 30,31, is reduced. However, the data processing unit 20 mayalso include another energy storage, such as for example an inductor orother suitable elements.

The data communication system, such as the example of a datacommunication system 1 shown in FIG. 1, may for example be used in anoccupant protection system. The occupant protection system may forinstance include a restraint system or other suitable type of protectionsystem. A restraint system generally refers to a system designed to holda person within the body of a vehicle and limit movement during a crash,thereby reducing severity of injury. The occupant protection system mayfor example include a data communication system in accordance with theinvention, such as the example shown in FIG. 1, and one or moreactuators connected to the central control unit 10 to actuate arestraint device. The restraint device may for example include anairbag, a seat belt pre-tensioning device or other restraint device.FIG. 6 schematically shows an example of a restraint system 60. Therestraint system 60 includes a restraint device 50, and an actuator 51.The actuator 51 is connected to the central control unit 10. As shown inFIG. 5, the central control unit 10 may include a controller 16 which isconnected to the data connection 30,31, for example via thesynchronisation unit 11 and can control the transmission of signalsbased on the data received from the data processing units 20,21. Forinstance, if the data processing units 20,21 transmit data whichindicates that an accident has happened, the controller 16 may decide tooutput an activation signal. The central control 10 may transmit theactivation signal to the actuator 51, which may for example be an airbagactuator. The actuator may actuate the restraint device 50 in responseto the activation signal. For example, if the data processing unit 20includes an acceleration sensor, the central control unit, in case thesensor or sensors senses an acceleration above a predeterminedactivation threshold, the central control unit 10 may transmit theactivation signal. In response to the activation signal, the actuator 51may then activate the restraint device 50, e.g. the airbag 50. In theexample of FIG. 6, only one restraint device 50 and actuator 51 areshown. However, the system 60 may include more than one restraint device50 and more than one actuator 51, which may be controlled separately bythe central control unit 10.

FIG. 7 shows an example of vehicle 70 provided with an occupantprotection system. The example shown in FIG. 8 includes restraintdevices, 50, in this example airbags, connected via a suitable dataconnection 40,41 to a data communication system 1, for instance theexample shown in FIG. 8. As explained with reference to FIG. 5, thecentral control unit 10 may be arranged to control the actuator 51 basedon data received from the data processing unit 20 and control actuationof the inflation of the airbags, thus protection the occupants of thevehicle 70 against impact, for example during a crash.

In the foregoing specification, the invention has been described withreference to specific examples of embodiments of the invention. It will,however, be evident that various modifications and changes may be madetherein without departing from the broader spirit and scope of theinvention as set forth in the appended claims. For instance, the dataprocessing units 20 may share the connection, e.g. the data connections30,31, to the central control unit 10. Thereby, the central control unitcan send the same synchronisation signal to the data processing units 20simultaneously. In the example of FIG. 1, as mentioned, the dataprocessing units 20 are connected to the central control unit 10 via abus-connection. As shown in the example of FIG. 1, for instance, thedata connections 30,31 may form a bus connection between the centralcontrol unit 10 and the, decentralized, data processing units 20. Thebus connection may for example be a parallel bus or a serial bus.However, other types of connections are also possible, such as forexample a point-to-point connection in which each data processing unit20 is connected by a separate connection to the central control unit 10.

Also, in the example of FIG. 5, the transistors T10,T20 are drawn asfield effect transistors, of which the gate G10,G20 is used as a controlterminal and the sources S10,S20 and drains D10,D20 are connected to thedata connection 30, voltage supply and ground respectively and formrespective signal terminals. However, other types of transistors, suchas bipolar transistors, may be used and be connected in a differentmanner to control the current drawn from the data connection and tocontrol the voltage of the data connection.

Also, the invention is not limited to physical devices or unitsimplemented in non-programmable hardware but can also be applied inprogrammable devices or units able to perform the desired devicefunctions by operating in accordance with suitable program code. Theinvention may also be implemented in a computer program for running on acomputer system, at least including code portions for performing stepsof a method according to the invention when run on a programmableapparatus, such as a computer system or enabling a programmableapparatus to perform functions of a device or system according to theinvention. Such a computer program may be provided on a data carrier,such as a CD-ROM or diskette, stored with data loadable in a memory of acomputer system, the data representing the computer program. The datacarrier may further be a data connection, such as a telephone cable or awireless connection.

The central control unit 10 and/or the data processing unit 20 may beprovided separately. It is also possible to provide a kit of parts, e.g.a central control unit 10 and one or more data processing units 20 whichcan be assembled into a data communication system 1, such as forinstance into the example of a system shown in FIG. 1.

Furthermore, the devices may be physically distributed over a number ofapparatuses, while functionally operating as a single device. Forexample, the central control unit 10 may be implemented as anarrangement of discrete components connected to each other to operate asthe central control unit 10. Also, devices functionally forming separatedevices may be integrated in a single physical device. For example, theelectrical circuit shown in FIG. 3 can be implemented in a singleintegrated circuit.

However, other modifications, variations and alternatives are alsopossible. The specifications and drawings are, accordingly, to beregarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other elements or steps then those listed in aclaim. Furthermore, the words ‘a’ and ‘an’ shall not be construed aslimited to ‘only one’, but instead are used to mean ‘at least one’, anddo not exclude a plurality. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

1. A data communication system, including: a data processing unit; acentral control unit; a data connection connecting said data processingunit to said central control unit; a power source at said centralcontrol unit to provide power to said data processing unit over saiddata connection; wherein said central control unit includes asynchronisation unit for outputting via said data connection asynchronisation signal to said data processing unit by changing thevoltage of said data connection from a steady state voltage level to asecond non-zero voltage level, the absolute value of the second voltagelevel being smaller than the absolute value of said steady state voltagelevel, said synchronisation signal not associated with a correspondingdischarging of said data connection subsequent to outputting saidsynchronisation signal; and wherein said data processing unit includes adata generator for generating data and transmitting said generated datato said central control unit as a pulsed current in response todetermining said voltage of the data connection has returned to thesteady state voltage level following said synchronisation signal.
 2. Adata communication system as claimed in claim 1, wherein said dataprocessing unit includes an energy storage connected to said dataconnection and to said data generator for releasing stored energy to thedata generator when said synchronisation signal is received by the dataprocessing unit.
 3. A data communication system as claimed in claim 1,wherein said data processing unit includes a signal inverter connectedto said data connection, said signal inverter outputting a signal of afirst level when said synchronisation signal is inputted to said signalinverter and outputting a signal of a second level when saidsynchronisation signal is not inputted to said inverter.
 4. A datacommunication system as claimed in claim 2, wherein said data processingunit includes a signal inverter connected to said data connection, saidsignal inverter outputting a signal of a first level when saidsynchronisation signal is inputted to said signal inverter andoutputting a signal of a second level when said synchronisation signalis not inputted to said inverter.
 5. A data communication system asclaimed in claim 1, wherein said data processing unit includes at leastone sensor, selected from a group consisting of an accelerationsensitive sensor and a pressure sensor.
 6. A data communication systemas claimed in claim 1, including at least one actuator unit connected tothe central control unit, and wherein said central control unit isarranged to control said at least one actuator unit based on datareceived from said data processing unit.
 7. An occupant protectionsystem, including a data communication system as claimed in claim 6, andat least one occupant protection device connected to said centralcontrol unit, wherein said central control unit is arranged to controlsaid occupant protection device based on data received from dataprocessing unit.
 8. A vehicle provided with an occupant protectionsystem as claimed in claim
 7. 9. A method for communicating data in adata communication system, said system including a data processing unit,a central control unit, and a connection connecting said data processingunit to said central control unit, the method comprising: providing viasaid data connection power to said data processing unit; periodicallyoutputting by said central control unit a synchronisation signal overthe data connection to the data processing unit interface by changingthe voltage of said data connection from a steady state voltage level toa second non-zero voltage level, the absolute value of the secondvoltage level being smaller than the absolute value of said steady statevoltage level, said synchronisation signal not associated with acorresponding discharging of said data connection subsequent tooutputting said synchronisation signal; transmitting by said dataprocessing unit data to the central control unit as a pulsed current inresponse to determining said voltage of the data connection has returnedto the steady state voltage level following said synchronisation signal.10. The method of claim 9, wherein said data processing unit includes anenergy storage connected to said data connection and to said datagenerator for releasing stored energy to the data generator when saidsynchronisation signal is received by the data processing unit.
 11. Themethod of claim 9, wherein said data processing unit includes at leastone sensor selected from a group consisting of an acceleration sensitivesensor and a pressure sensor.
 12. The method of claim 9, wherein saidcentral control unit is coupled to at least one actuator unit, andwherein said central control unit is arranged to control said at leastone actuator unit based on data received from said data processing unit.13. The method of claim 9 wherein said at least one actuator unit iscoupled to at least one occupant protection device, and wherein saidcentral control unit is arranged to control said occupant protectiondevice based on data received from said data processing unit.